1. Field of the Invention
The present invention relates to a catalyst component for use in the polymerization of alpha-olefins. More specifically, the present invention relates to a catalyst component for the polymerization of alpha-olefins and a catalyst for the same comprising the catalyst component, which make it possible to produce alpha-olefin polymers having a high melting point, and to a process for producing alpha-olefin polymers using the catalyst.
2. Related Art
The so-called Kaminsky catalysts (metallocene catalysts) are well known as homogeneous catalysts for the polymerization of olefins. These catalysts are characterized in that they have extremely high polymerization activity and that they are useful for the production of polymers having a narrow molecular-weight distribution.
Ethylenebis(indenyl)zirconium dichloride and ethylenebis-(4,5,6,7-tetrahydroindenyl)zirconium dichloride have been known as transition-metal compounds which are used when isotactic polyolefins are produced by the use of the Kaminsky catalysts (Japanese Laid-Open Patent Publication No. 130314/1986). However, these compounds appear to have shortcomings in that the polyolefins obtained have a low molecular weight and that when the polymerization is carried out at low temperatures, high-molecular-weight polyolefins can be obtained, but the compounds cannot show high polymerization activity. Further, it has also been known that polyolefins having a high molecular weight can be obtained when those compounds which are prepared by replacing the zirconium in the above transition-metal compounds with hafnium are used (Journal of Molecular Catalysis, 56 (1989), pp. 237-247). However, this method seems to he disadvantageous in that high polymerization activity would not be expected.
Furthermore, dimethylsilylenebis-substituted cyclopenta-dienylzirconium dichloride and the like were proposed in Japanese Laid-Open Patent Publication No. 301704/1989, Polymer Preprints, Japan, Vol. 39, No. 6, pp. 1614-1616 (1990) and Japanese Laid-Open Patent Publication No. 12406/1991, and dimethylsilylenebis(indenyl)zirconium dichloride and the like were proposed in Japanese Laid-Open Patent Publications Nos. 295007/1988 and 275609/1989. By these catalysts, it was made possible to obtain highly-stereoregular polymers having a high melting point if the polymerization is carried out at relatively low temperatures. However, when polymerization is carried out under the condition of higher temperatures, which is economically advantageous, the polymers obtained would have a stereoregularity, a melting point and a molecular weight significantly lowered. For this reason, it is demanded to improve the catalysts.
Japanese Laid-Open Patent Publications Nos. 268307/1992 and 268308/1992 suggest that the stereoregularity and molecular weight of polymers can be improved to some extent when use is made as a catalyst of a compound having a substituent attached at a site next to the site of the crosslinking group (the 2-position) in the above-described cyclopentadienyl compound. Further, Japanese Laid-Open Patent Publications Nos. 300887/1992, 306304/1993, 100579/1994, 184179/1994 and 157661/1994 suggest that polymers having improved properties can be obtained when use is made as a catalyst of a metallocene compound having a substituent attached to the indenyl group. However, the properties of those polymers which are produced by the use of these substituted compounds under the polymerization condition of elevated temperatures, which condition is economically advantageous, are seemed to be still insufficient.
An object of the present invention is to provide a catalyst component for the polymerization of alpha-olefins and a catalyst for the same, which make it possible to produce, in high yield, high-molecular-weight olefin polymers capable of being extrusion- or injection-molded, having a high melting point, and a process for producing alpha-olefin polymers.